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Flashcards in RT 205 Electromagnetism II Deck (54):
1

Faraday's Law: Methods to induce a current:

1. Moving a permanent magnet into and out of a coil of wire also induced a current in the wire while the magnet was in motion.
2. Moving a conductor near a stationary permanent magnet caused a current to flow in the wire, too, as it was moving.
3. Made it possible to determine the direction of the induced current flow.

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2

Four factors of Faraday's Law: The magnitude of the induced current depends on four factors.

1. The strength of the magnetic field
2. The velocity of the magnetic field as it moves past the conductor
3. The angle of the conductor to magnetic field (lines of flux)
4. The number of turns in the conductor

3

Lenz's Law
An induced emf generates a current that induces a counter magnetic field that opposes the magnetic field generating the current. Name the law.

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4

The production of an electromotive force (emf) or voltage in an electric circuit caused by a changing magnetic flux in a neighboring circuit

Mutual Induction

5

Property whereby an electromotive force is induced in a circuit by a variation of current in the circuit itself

Self Induction

6

Opposition to the flow of AC current produced by an inductor; measured in ohms and varies in direct proportion to frequency

Inductive Reactance

7

Fleming's Right Hand Generator Rules
Thumb: points in direction of conductor (armature) moves
Index finger: points in the direction of magnetic lines of force
Middle finger: Indicates the direction of conventional current flow

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8

Converts mechanical energy into electrical energy

Dynamo (Generator)

9

How is electricity produced in a dynamo?

From magnets whirling inside of coils of wire in the generator core.

10

Components of a Generator
Moving part of magnetic device consisting of one or more coils that are electrically connected to create a rotational section of a generator

Armature (Conductor)

11

Components of a Generator
Means of producing an electrical connection through a rotational assembly

Slip Rings

12

Components of a Generator
Conducts current between rotating stationary parts of a generator or motor

Brushes

13

Produced when wires motion relative to the lines of force is reversed

Alternating Current

14

1 Cycles per second (cps)= 1 Hz

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15

U.S. Generators utilize how many Hertz?

60 Hz (or 120 Changes per second)

16

Components of a Generator
A single ring that is divided in half, with each half connected to one end of the armature wire (Replaces pair of slip rings, produced direct current, keep current flowing in the same direction)

Commutator Ring

17

Converts electrical to mechanical energy

Motors

18

Fleming's Left Hand Motor Rule
Thumb: Movement of Conductor on Rotor
Index: Magnetic lines of force field
Middle: Current or electron flow

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19

What type of rings do AC motors use?

Slip Rings

20

What type of rings do DC motors use?

Commutator rings

21

Types of motors
Synchronus Induction
Induction motor electromagnets that turn the anode; Supplied with multiphase current

Stator

22

Types of motors
Synchronus Induction
A hollow copper cyclinder or cuff that is attached to the anode disk by a molybdenum shaft (Used in rotating anode x-ray tubes)

Rotor

23

Measures Direct Current (Use permanent magnets)

Galvanometers

24

Measures Alternating Current (Use electromagnets)

Ammeter

25

Measures connected in parallel (Measure potential difference)

Voltmeter

26

A device in which two coils are placed near one another without electrical connection (The number of turns in the coils differs, causing a change in current in the secondary coil; Serves to either increase or decrease the voltage)

Transformers

27

Three causes of loss of efficiency in transformers:
First cause:Copper loss (I^2R loss)
1. Resistance in the wires (minimized by using low resistance wire.
2. Large diameter copper (Minimized by using high voltage and low amperage)

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28

Three causes of loss of efficiency in transformers:
Second cause: Hysteresis loss (lagging loss)
1. Results from energy expended as the continually changing AC current magnetizes, demagnetizes, and remagnetizes the core

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29

Three causes of loss of efficiency in transformers:
Third cause: Eddy current loss
1. Currents that oppose the magnetic field that induced them (laminating the core reduces this loss)

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30

Accumulates and stores an electrical charge (Two oppositely charged metal plated separated by dielectric)

Capacitors

31

A material that can sustain an electric field but does not conduct electric current

Dielectric

32

Capacitor Formula:
C= Q/V
C= capacitance of the capacitor
Q= charge on one of the plates of the capacitor
V= voltage across the capacitor

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33

What is capacitance measure in?

farads (F)

34

1F= 1Coulomb/Colt
This means how many coulombs of charge can be stored in a capacitor per volt in the power source

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35

The process of converting alternating current into a unidirectional current, by removing or inverting that part of the wave laying on one side of the zero amplitude axis

Rectification

36


A solid-state switching device for semiconductors to convert AC current in one of two directions controlled by an electrode
(Thyristor or silicon-controlled rectifier (SCR))

Solid-state diodes

37

A device that allows current to flow in one direction only (Produced by sandwiching n-type and p-type crystals

Diode

38

A cathode and anode separated so that electrons can only flow from cathode to anode

Vacuum tube type diode

39

Flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. The effect increases dramatically with increasing temperature (1000- 3000 K)

Thermionic Emmission

40

Another name for Thermionic emission?

Space charge cloud

41

Protects from current that can damage equipment?

Rectification

42

Rectifying process
Passes only one-half of each incoming sinusoid, and does not pass the opposite half cycle

Half-wave Rectification

43

Rectifying process
Passes the positive half and inverts the negative half cycle of the input sinusoid so that the output contains two half sine pulses for each input cycle

Full-wave Rectification

44

Main Circuit Parts of an x-ray machine:
The switch that generates the power to the x-ray tube

Main Switch

45

Main Circuit Parts of an x-ray machine:
A remote control device that permits current flow through the circuit

Exposure Switch

46

Main Circuit Parts of an x-ray machine:
Device used to end the exposure at an accurately measured preset time

Timer

47

Main Circuit Parts of an x-ray machine:
Where the alternating current comes form to power the circuit

Main breaker

48

Main Circuit Parts of an x-ray machine:
This is where you adjust the kVp for the exposure

Autotransformer

49

Main Circuit Parts of an x-ray machine:
This transformer bumps the voltage up so that the x-ray tube has very high voltage to make the electrons have enough energy to form x-rays

High-voltage step-up transformer

50

Main Circuit Parts of an x-ray machine:
This makes the current only go in one direction through the x-ray tube

Four-diode rectification circuit

51

Main Circuit Parts of an x-ray machine:
This variable resistor adjusts the current going to the filament

Filament circuit variable resistor

52

Main Circuit Parts of an x-ray machine:
This transformer steps the voltage down and therefore the current up.

Filament step-down transformer

53

Main Circuit Parts of an x-ray machine:
This is where the x-rays are created

X-ray tube

54

Main Circuit Parts of an x-ray machine:
This rotates the anode

Rotor Stator